<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            width: 200px;
            height: 200px;
            background-color: aqua;
        }
        button{
            margin-top: 20px;
            width: 100px;
            height: 20px;
        }
    </style>
</head>
<body>
    <div id="box"></div>
    <button>点我变色</button>
    <script>
        let div = document.querySelector('div')
        let btn = document.querySelector('button')
        btn.addEventListener('click',function(){
            div.style.backgroundColor = 'pink'
        })
    </script>
</body>
</html>